Conventionally, refrigeration apparatuses include a refrigeration cycle composed of a compression section, a gas cooler, a throttle section, and the like. Refrigerant compressed in the compression section radiates heat in the gas cooler, and is then decompressed in the throttle section so that the refrigerant evaporates in the evaporator. As the refrigerant evaporates, surrounding air is cooled.
In recent years, the refrigeration apparatuses of this type have been inhibited from using chlorofluorocarbon-based refrigerant because of natural environmental issues and the like. Accordingly, refrigeration apparatuses have been developed which use carbon dioxide that is natural refrigerant as a substitute of the chlorofluorocarbon-based refrigerant. The carbon dioxide refrigerant, which is refrigerant having large difference between high and low pressures, is known to have a low critical pressure, so that the high-pressure side of a refrigerant cycle is in a supercritical state when the carbon dioxide refrigerant is compressed (see, for example, PTL 1).
Heat pump apparatuses that constitute water heaters also increasingly use the carbon dioxide refrigerant which can provide a good heating effect in the gas cooler. In some development of such heat pump apparatuses, the refrigerant that comes out of the gas cooler is expanded in two stages, and a gas-liquid separator is provided between each expansion apparatus so that gas can be injected into a compressor (see, for example, PTL 2).
In refrigeration apparatuses that cool the inside of a chamber using an endothermic action in an evaporator disposed in such places as showcases, the temperature of refrigerant at an outlet of a gas cooler may increase due to the reasons such as outside air temperature (heat source temperature on the gas cooler side) being high.
In this case, specific enthalpy at an inlet of the evaporator increases, so that refrigeration performance considerably deteriorates. Accordingly, in order to solve the problem, discharge pressure (high pressure-side pressure) of a compression section may be increased. However, this causes another problem of decreased coefficients of performance due to increased compression power.
Accordingly, refrigeration apparatuses that implement a refrigeration cycle called a split cycle have been proposed (see, for example, PTL 3). In the split cycle, the refrigerant cooled by a gas cooler is diverged into two refrigerant flows. One of the diverged refrigerant flows is throttled with an auxiliary throttle section, and is then allowed to flow through one channel of a split heat exchanger, while the other refrigerant flow is allowed to flow through the other channel of the split heat exchanger to perform heat exchange. The other refrigerant flow is then guided into an evaporator through a main throttle section.
According to such an refrigeration apparatus, one refrigerant flow that is decompressed and expanded by the auxiliary throttle section can cool the other refrigerant flow, so that the specific enthalpy at the inlet of the evaporator can be decreased. As a result, the refrigeration performance can be enhanced.